Explosion detecting means for a fluid pipeline

ABSTRACT

A device for detecting an increase in water flow through a water service main and for detecting the pressure drop existing in the water flowing through the main is disclosed. The device operates when the volume of the existing water flow in the main exceeds by a predetermined value a volume of water flow previously stored in a first memory device during a predetermined sampling period. The apparatus for detecting the pressure drop of the water in the water service main operates when the amplitude of the existing water pressure falls below the water pressure previously stored in a second memory device. The supply of water into the water service main is stopped by the simultaneous operation of both these detecting devices.

United States Patent Inventor Appl. No.

Filed Patented Assignee Priority Takehiko Tomita Tokyo, Japan 881,103

Dec. 1, 1969 Dec. 21, 197 1 Tokyo Shibaura Electric Co., Ltd.Kawasaki-shi, Japan Dec. 10, 1968 Japan 43/90067 EXPLOSION DETECTINGMEANS FOIR A FLUIID PIPELINE 8 Claims, 1 Drawing Fig.

US. Cl 1137/460, 137/4875, 137/565 Int. Cl F16k17/20 Field of Search137/565,

Primary Examiner-William R. Cline Atl0rney-Oblon, Fisher dc SpivalcABSTRACT: A device for detecting an increase in water flow through awater service main and for detecting the pressure drop existing in thewater flowing through the main is disclosed. The device operates whenthe volume of the existing water flow in the main exceeds by apredetermined value a volume of water flow previously stored in a firstmemory device during a predetermined sampling period. The apparatus fordetecting the pressure drop of the water in the water service mainoperates when the amplitude of the existing water pressure falls belowthe water pressure previously stored in a second memory device. Thesupply of water into 43 the water service main is stopped by thesimultaneous operation of both these detecting devices.

iii-3 i i 1 1 9 COMPA- COMPA RATOR RATOR L 1? H MEMORY MEMORY CIRCUITC|RCU|T 17 2O SAMPLING SAMPLING CIRCUIT CIRCUIT 2 6 27 PRESSURE SAMPLINGTRANSDU PULSE CER GENERATOR I; n K 25 CITY WATER WORKS MOTOR CONTROL I II ATENTEU m L i k coMPA- GGMPA- RATGR RAToR MEMORY MEMGRY cIRcuIT cIRcuIT SAMPLING SAMPLING cIRcuIT cIRcuIT 2 PRESSURE SAMPLING TRANSDU-PULSE CER GENERATO 15 I3 I if! Ea VALVE CITY vI/ATER CONTROL WORKS IMoToR coNTRoL 28 TI. 3 INVENTO BY lI MAW/U9)- W/kMX/E II F, 7 11EXPLOSION DETECTING MEANS FOR A FLUID PIPELINE BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates toexplosion, or rupture detecting means for fluid pipe lines, andparticularly to means for accurately detecting a rupture in a city waterservice main.

2. Description of the Prior Art In a large city, there are frequentlylarge construction projects for subways, roads, new buildings and thelike during which water service mains buried beneath the earth may beruptured by piles which are driven into the earth. Once such a ruptureoccurs, large areas of the city near the damaged portion of the waterservice main may be flooded or shut 05 from their water supply.Accordingly, it is important to provide means for rapidly detecting therupturing of water mains to rapidly prevent the leakage of watertherefrom.

For this purpose, there have been known two representative types ofdevices in the prior art, one of which detects a sudden increase ofwater flow in a water service main upon the occurrence of a rupture, andthe other of which detects a sudden decrease of pressure in the rupturedmain. The former, however, has a significant defect in the fact that itmay respond to a momentary sudden increase of initial flow at the startof pumping. The latter devices require troublesome readjustments fromtime to time, with respect to their triggering threshold, because of theincrease of passage resistance in the water service main which resultsfrom rust accumulating on the inner surface thereof for a long period.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide improved explosion or rupture detecting means for water servicemains which is not falsely triggered by a sudden increase of water flowin the water service main caused by pump starting, for example, and doesnot require extremely troublesome readjustments of its referencethreshold for long term pressure drops.

Briefly, in accordance with one aspect of the present invention, thereare provided a pair of transducers in a water service main, one of whichfunctions to convert water flow in the water service main into firstelectrical signals and the other of which acts to convert pressure dropsexisting in the main into second electrical signals. The firstelectrical signals are directly fed to one input of a first comparatorto suppress the operation thereof, and the same signals are fed to theother input of the same comparator with a time delay through a firstsampling circuit and a first memory circuit to operate the comparator.The aforesaid time delay of the first signals depends upon the samplingperiods of the first sampling circuit. Similarly, second electricalsignals are directly fed to one input of second comparator and are alsofed to the other input of the second comparator with a delay timethrough second sampling circuit and a second memory circuit to operatethe second comparator. The delay time of the second signals depends onthe sampling periods of the second sampling circuit. It is preferablethat there is provided a common sampling signal generator for bothsampling circuits to synchronize the output signals of the comparators.The output signals of the comparators are connected in series to form anAND gate thereby to cause a pump and/or a main valve for the waterservice main to stop and/or shut off.

BRIEF DESCRIPTION OF THE DRAWINGS The single FIGURE is a block diagramillustrating the preferred embodiment of the present invention.

Referring now to the FIGURE, there is shown a pump set generally denotedby reference numeral which comprises a pump 11 driven by an electricalmotor 12. The pump 11 pumps stored water into a water service main 13through a main stop valve 14. The end of the water service main 13 isconnected to a water distributing network for a city.

To measure the water flow, there is provided a flowmeter I5 in the waterservice main, which may preferably be an electromagnetic flowmeter.Thus, electrical signals proportional to the water flow in the waterservice main are generated by the electromagietic flowmeter. Theflowmeter 15 is the first transducer described above. The water servicemain has also a second transducer 26 which acts to convert the waterpressures in the main to appropriate electrical signals.

The electrical signals derived from the flowmeter are directly fed toone input of a comparator 16. The output signals of the flowmeter I5 arealso fed to a sampling circuit 117 and then stored in a memory circuit1% during every sampling period of the sampling circuit. The memorycircuit W is cleared every sampling period and at the same time storesthe successive sampling signals. These sampling signals are finally fedto the other input of the comparator 16 and compared with the directsignals at the comparator. Thus, it will be understood that the sampledsignals lag by a sampling period of time defined by the sampling circuit117. The comparator 16 generates an output signalonly when thedifference between the sampled signals and the direct signals increasesto a predetermined value. Thus, it can be seen that the direct signalsfunction as operating signals whereas the sampled ones function assuppressing signals. The output signals of the comparator 16 areemployed to close a normally open contact 16a. Thus, in other words, theclosing of the output contact 16a of the comparator 16 will occur onlywhen the present flow existing in the water service main becomes largerby a predetermined value than the previously measured flow which hadexisted in the prior sampling period. Accordingly, for example, if thesampling period is selected as 1 minute, the closing of the contact 16adue to the normal open and closing operations of remote valves (notshown) located anywhere on the service main will not occur because thesevalves are opened and closed gradually over periods of 2 or 3 minutes.However, if the source pump 11 starts, the contact 16a may be closederroneously because of a large increase in the rate of water flow.

This defect can be effectively eliminated by the following arrangements.As described above, the water service main I3 is provided with a secondtransducer 26 which acts to convert the pressure of water in the waterservice main to electrical signals. The electrical pressure signals aredirectly fed to an input of a second comparator l9 and are also fed to asampling circuit 20, and then to an input of a memory circuit 2llwherein they are stored. The stored pressure signals are then fed to theother input of the comparator 19.

Since the operations of comparator l9, sampling circuit 20 and memorycircuit 21 are identical to those as described in connection with theflow-measuring system, the detailed explanation thereof is omitted. Thecomparator 1'9 also has a normally open contact connected in series withthe aforesaid normally open contact 16a. The comparator 119 causes thecontact ll9a to close only when the amplitude of the pressure existingin the water service main becomes lower by a predetermined amount thanthe pressure amplitude stored in the memory circuit. Accordingly, whenan explosion or rupture of the water service main occurs, the pressuresignals which come directly into one input of the comparator will bereduced due to the rupture of the main. The sampled and stored pressuresignals will then be greater than the directly received pressure signalsso as to close: the contact 11911. The contact Ha forms an AND gate withthe contact 160. It can be seen that it is difiicult to satisfactorilyprovide a reliable system where only a pressure responsive device isprovided because such a device can not distinguish a relatively rapidpressure drop due to a rapid increase in water demand from a pressuredrop resulting from a rupture of the water service main. However, thisdefect is effectively eliminated in the present invention by the use ofsampling periods which are short relative to the operating speeds ofremote values.

One end 22 of the AND gate fomied by the series connected contacts 16aand 19a is connected to one of the terminals of a control voltage source(not shown) and the other end thereof is connected to an alarm device23, a control device 24 for an electric motor 12 and a control device 25for a main valve 14. 4

Under normal operating conditions, the control device 24 is constructedin such a manner as to apply variable voltages to the electric motor 12from a relatively constant AC voltage source 28, thereby controlling thepump speeds as desired. The control device 24 also includes anarrangement which acts to deenergize the motor when it receives anoverride signal through the series connected contacts 16a and 19a. Thecontrol 25 for the main valve 14 is constructed to the valve undernormal operating conditions, but includes an arrangement to make thevalve close when it receives an override signal through the seriesconnected contacts 16a and 19a as described above.

There is also provided a sampling pulse generator 27 for generating apulse train for controlling the sampling circuits l7 and 20 periodicallyand simultaneously. As described above, the pulse repetition rate of thepulse train may be selected to about one minute, which is shorter thanthe two or three minute period during which remote valves of the waterservice main would normally be operated.

The operation of the system will now be described in variouscircumstances. Assume first that'the pump set begins to perform thepumping-up operation and the main valve 14 is opened to pump the waterinto the water service main 13. The water flow and the pressure in thewater service main gradually increase until they reach normal runningvalues. The comparator 16 may operate to close the contact 16a thereofin response to the increased rate of water flow. However, the outputcontact 19a of the comparator 19 will not close, because the waterpressure in the water service main is increasing during the startingperiod of the pump 11 whereby the amplitudes of pressure signals storedin the memory circuit 21 will exceed the present water pressure levelexisting in the water service main. Consequently, there is no chancethat contacts 160 and 19a will be simultaneously closed erroneously bythe starting of pump 11. In this way, the pumping system will reach itsnormal operating state.

During normal operation of the pumping system, the pumping set 10operates at variable speeds through motor control 24 in response to thedemand for water, as is well known in the art. Assume now that anincrease of water demand has occurred with a relatively high rate ofchange, which may be due to the opening of a large remote valve locatedin the water service main in a remote area. There will then occur apressure drop at a relatively high rate in the water service main inresponse to this increase in water demand. As described above, althoughthese changes tend to close the contacts 160 and 19a, their rate ofchange is longer than the sampling period defined by the pulse train ofthe sampling pulse generator, and consequently the contacts 16a and 19acan not close to erroneously operate the alarm and the controls for thepump set and the main valve.

If an explosion or rupture occurs in the water service main, the waterflow through the water service main will rapidly increase and at thesame time the water pressure in the main will drop. it will be readilyunderstood that the rate of change of these events falls within thesampling period of the sampling circuits l7 and 18. Thus in this case,if the existing water flow exceeds the amplitude stored in memorycircuit 18 by a predetermined amount and at the same time the waterpressure drops below the amplitude stored in memory circuit 19, bothcomparators 16 and 19 simultaneously cause the contacts 16a and 19a toclose. An override signal is thus developed through both closed contacts16a and 19a to the alarm 23 to announce the occurrence of the fault, andto the control 25 to shut off the main valve 14, as well as to thecontrol 24 to stop the pump set 10. Thus, it is possible to rapidly stopthe water supply to the water service main thereby causing the amount ofwater which leaks therefrom to be effectively reduced.

As described above, in accordance with this invention, it is possible toprovide a rupture detecting means for accurately detecting an explosionor rupture of a city water service main, which has the followingadvantages. Firstly, since dead bands are provided in the responsecharacteristics of both comparators 16 and 19, respectively, they do notoperate erroneously, in response to the normal fluctuations in waterflow and water pressure in the water service main. Secondly, when thepumping set starts causing a rapid increase in water flow, even thoughthe first comparator 16 which responds to the increase of water flow mayoperate erroneously, the stop control of the pumping set is notactivated because of the second comparator which responds only todecreased pressure in the water service main. Thirdly, it is possible toeasily prevent the comparators from erroneous operation due to normalvariations in water flow and water pressure which may occur during theopening and closing of remote valves because the sampling periods forboth sampling circuits have been so selected that they are shorter thanthe opening and closing speeds of the remote valves. Lastly, becauseboth sampling circuits are energized from a common sampling signalgenerator, and are operated in synchronism each other, there is nochance to simultaneously make both contacts close, and thus the rupturedetection may be accurately efiected.

It will be readily appreciated by those skilled in the art that bothcontacts 16a and 19a may be alternatively arranged as normally closedcontacts connected in parallel to form an OR gate, thus causing thecontrols 24 and 25 to stop the pump set 10 and close the main valve 14only when both contacts are simultaneously open. Though the contacts 16aand 19a have also been shown as mechanical switches, they may, ofcourse, also be contactless or transistorized switches. Further, thespirit of the present invention may be adapted for detecting explosionsor ruptures in pipe lines used in the petroleum industry or in any othertypes of pipelines.

Obviously, numerous additional modifications and variations of thepresent invention are possible in light of the above teachings. It istherefore to be understood that within the scope of the appended claimsthe invention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by letters patent ofthe United States is:

1. A system for detecting ruptures in a pipeline comprising: fluid flowresponsive means coupled to said pipeline for generating signalsproportional to the rate of fluid flow in said pipeline, first logicmeans coupled to said fluid flow responsive means for generating anoutput 'signal only if fluid flow in said pipeline is increasing at arate greater than a predetermined rate, fluid pressure responsive meanscoupled to said pipeline for generating signals proportional to fluidpressure within said pipeline, second logic means coupled to said fluidpressure responsive means for generating an output signal only ifpressure in said pipeline is decreasing at a rate greater than apredetermined rate; and, control means coupled to said first and secondlogic means for generating a control 'signal in response to thesimultaneous presence of output signals from both said first and secondlogic means. 2. A system for detecting ruptures in a pipeline as inclaim 1, further comprising:

means coupled to said control means and to said pipeline for cutting offfluid flow in said pipeline in response to the generation of saidcontrol signal. 3. A system for detecting ruptures in a pipeline as inclaim 1, wherein:

said control means comprises an AND gate including two series connectedswitching means. 4. A system for detecting ruptures in a pipeline as inclaim 1 further comprising:

alarm means coupled to said control means for producing pressureresponsive means.

an alarm signal in response to the generation of said con- 7. A systemfor detecting ruptures in a pipeline as in claim 5, trol signal.wherein: 5. A system for detecting ruptures in a pipeline as in claim 1,said first memory means includes wherein: a memory circuit; and,

said first logic means comprises memory means coupled to sampling meanscoupled to said memory circuit and to said said fluid flow responsivemeans for storing an output fluid flOW lBSpOllSiVE means for clearingand reloading signal thereof for a predetermined interval; and, Saidmemory circuit and for transferring said stored signal comparator meansl d to id memory means d to from said first memory means to saidcomparator means said fluid flow responsive means for comparing said atpledetel'lnlmd time Intervalstored signal with another output signalfrom said fluid System for detectmg ruptures a P P- Claim 5, flowresponsive means. whefemi 6. A system for detecting ruptures in apipeline as in claim 5, Said sewndynerfwry means Includes wherein; i g amemory circuit; and,

said second logic means comprises memory means Coupled l5 sampling meanscoupledto said memory circuit and to said to said fluid pressureresponsive means for storing an outfl Pressure f f means for cleanf'lgreloadput signal thereof forapredetermined interval; and, Said memqy andfor transferring 531d stored comparator means coupled to said memorymeans and to S'gnal from Sam] Second f "l to sald compara' said fluidpressure responsive means for comparing said tor means at a predetermmedintervalstored signal with another output signal from said fluid

1. A system for detecting ruptures in a pipeline comprising: fluid flowresponsive means coupled to said pipeline for generating signalsproportional to the rate of fluid flow in said pipeline, first logicmeans coupled to said fluid flow responsive means for generating anoutput signal only if fluid flow in said pipeline is increasing at arate greater than a predetermined rate, fluid pressure responsive meanscoupled to said pipeline for generating signals proportional to fluidpressure within said pipeline, second logic means coupled to said fluidpressure responsive means for generating an output signal only ifpressure in said pipeline is decreasing at a rate greater than apredetermined rate; and, control means coupled to said first and secondlogic means for generating a control signal in response to thesimultaneous presence of output signals from both said first and secondlogic means.
 2. A system for detecting ruptures in a pipeline as inclaim 1, further comprising: means coupled to said control means and tosaid pipeline for cutting off fluid flow in said pipeline in response tothe generation of said control signal.
 3. A system for detectingruptures in a pipeline as in claim 1, wherein: said control meanscomprises an AND gate including two series connected switching means. 4.A system for detecting ruptures in a pipeline as in claim 1, furthercomprising: alarm means coupled to said control means for producing analarm signal in response to the generation of said control signal.
 5. Asystem for detecting ruptures in a pipeline as in claim 1, wherein: saidfirst logic means comprises memory means coupled to said fluid flowresponsive means for storing an output signal thereof for apredetermined interval; and, comparator means coupled to said memorymeans and to said fluid flow responsive means for comparing said storedsignal with another output signal from said fluid flow responsive means.6. A system for detecting ruptures in a pipeline as in claim 5, wherein:said second logic means comprises memory means coupled to said fluidpressure responsive means for storing an output signal thereof for apredetermined interval; and, comparator means coupled to said memorymeans and to said fluid pressure responsive means for comparing saidstored signal with another output signal from said fluid pressureresponsive means.
 7. A system for detecting ruptures in a pipeline as inclaim 5, wherein: said first memory means includes a memory circuit;and, sampling means coupled to said memory circuit and to said fluidflow responsive means for clearing and reloading said memory circuit andfor transferring said stored signal from said first memory means to saidcomparator means at a predetermined time interval.
 8. A system fordetecting ruptures in a pipeline as in claim 5, wherein: said secondmemory means includes a memory circuit; and, sampling means coupled tosaid memory circuit and to said fluid pressure responsive means forclearing and reloading said memory circuit and for transferring saidstored signal from said second memory means to said comparator means ata predetermined time interval.